fixup! Bug 41459: WebRTC fails to build under mingw (Part 2)

Reworked the _com_error conversion to string, to use functions that are
available also to mingw.

third_party/libwebrtc/modules/desktop_capture/win/desktop_capture_utils.cc

@@ -10,7 +10,9 @@
 
 #include "modules/desktop_capture/win/desktop_capture_utils.h"
 
-#include "rtc_base/strings/string_builder.h"
+#include <cstdio>
+#include <cstdlib>
+#include "stringapiset.h"
 
 namespace webrtc {
 namespace desktop_capture {
@@ -20,11 +22,16 @@ namespace utils {
 std::string ComErrorToString(const _com_error& error) {
   char buffer[1024];
   rtc::SimpleStringBuilder string_builder(buffer);
-  // Use _bstr_t to simplify the wchar to char conversion for ErrorMessage().
-  _bstr_t error_message(error.ErrorMessage());
-  string_builder.AppendFormat("HRESULT: 0x%08X, Message: %s", error.Error(),
-                              static_cast<const char*>(error_message));
-  return string_builder.str();
+  string_builder.AppendFormat("HRESULT: 0x%08X, Message: ", error.Error());
+#ifdef _UNICODE
+  WideCharToMultiByte(CP_UTF8, 0, error.ErrorMessage(), -1,
+                      buffer + string_builder.size(),
+                      sizeof(buffer) - string_builder.size(), nullptr, nullptr);
+  buffer[sizeof(buffer) - 1] = 0;
+#else
+  string_builder << error.ErrorMessage();
+#endif
+  return buffer;
 }
 
 }  // namespace utils

third_party/libwebrtc/rtc_base/win/create_direct3d_device.h

@@ -11,8 +11,18 @@
 #ifndef RTC_BASE_WIN_CREATE_DIRECT3D_DEVICE_H_
 #define RTC_BASE_WIN_CREATE_DIRECT3D_DEVICE_H_
 
-#include <windows.graphics.directX.direct3d11.h>
+#include <windows.graphics.directx.direct3d11.h>
+#ifndef __MINGW32__
 #  include <windows.graphics.directX.direct3d11.interop.h>
+#else
+#  include <dxgi.h>
+#  include <inspectable.h>
+extern "C" {
+// This function is only used in decltype(..)
+HRESULT __stdcall CreateDirect3D11DeviceFromDXGIDevice(
+    ::IDXGIDevice* dxgiDevice, ::IInspectable** graphicsDevice);
+}
+#endif
 #include <winerror.h>
 #include <wrl/client.h>